Peculiarities of the Mechanical Response of Sapphire under Nanoindentation

The nucleation of dislocations in sapphire of various structural perfection has been investigated by nanoindentation. The studies were carried out on crystallographic planes С (0001), a (1 1 2 0), R (0 112). In the curve of indentation of a Berkovich indenter into the single crystals, an abrupt transition from elastic to plastic deformation has been observed at a depth of about 75 nm due to the nucleation of dislocations in the initially dislocation free region under the contact. Deterioration of structural perfection results in a decrease in shear stresses under which dislocations nucleated. It is shown that the anisotropy of sapphire nanohardness is less pronounced than the static one.